Adequate hydration is particularly important for comfortable air travel, especially aboard modern, very large, long range aircraft capable of flights of 20 or more hours duration. Typically, water is distributed to galleys, lavatories, and drinking water outlets of the aircraft to provide drinking water to passengers, to provide water for food and beverage preparation, and to provide water for personal hygiene (e.g., face and hand rinsing, teeth cleaning, etc.) during flights. Aircraft typically are crowded with thousands of passengers including babies, small children, handicapped people, possibly ill people, and others, from varied backgrounds, passing through a commercial passenger aircraft during a single week. Both passengers and crews contribute to microorganism populations aboard aircraft, and special precautions must be taken to minimize and avoid the possibility of bacteria, viruses, pathogenic cysts, and other microorganisms being transferred among passengers through the water distribution system. Further, water is supplied to aircraft from many locations and varies widely in taste and sanitary quality. In addition to point-of-use effective on-board drinking water microfilters/purifiers, a primary sanitation defense mechanism against bacteria and viruses is to maintain an adequate residual of chlorine, preferably free chlorine, within the water storage and distribution systems. Further, effective on-board point-of-use drinking water microfilters/purifiers reliably remove parasitic cysts (leading causes of water borne disease worldwide) such as Giradia and Crypto which are not controlled by chlorination.
Typically, a water distribution system on aircraft comprises a water storage tank supplying a centralized distribution line with various branches or legs extending from the central distribution line to locations throughout the aircraft. For example, water is distributed via the water distribution system to galleys, lavatories, and other locations as needed for food and beverage preparation, and for personal hygiene during flights. Galleys include many “service points” such as coffee makers, water boilers, and drinking water outlets. Similarly, lavatories often include drinking water outlets and may be used for face and hand rinsing, cleaning teeth and short term personal medication. There are many possible opportunities for aircraft drinking water systems/supplies to become contaminated with microorganisms even if hygienically safe when loaded aboard an aircraft.
Typically, water filter/purifier units (e.g., a water filter or a water purifier), each comprising a housing (e.g., a pressure vessel) and a filtration/purification cartridge contained in the housing for filtering and/or purifying water, are installed in or near galleys and lavatories on water lines of the water distribution system as part of the aircraft water distribution system to filter and/or purify the water passing through the water filter/purifier units to improve water quality for consumption and for food and beverage preparation. Water purifiers (water filter/purifiers having a purification element) must be independently certified to meet the EPA Guide Standard Protocol for Microbiological Purifiers relative to bacteria, viruses and cysts. Structured Matrix™ purifiers, sold by General Ecology, Inc., also provide excellent filtration. Filters, such as General Ecology, Inc.'s Structured Matrix™ microfilters or simple, fine, or coarse carbon and/or sediment systems, may be sophisticated, but such filters cannot legally be referred to as microbiological purifiers before being verified that they meet the EPA Guide Standard Protocol for Microbiological Purifiers. Space in galley and lavatory compartments is expensive and severely limited. Accordingly, water filter/purifier units usually are installed in “out of the way”, often difficult to access locations often behind other more readily accessible equipment and bulkheads.
Possible microorganisms of concern are pathogenic bacteria, cysts and viruses. Chlorine resistant pathogenic cysts such as Crypto require special consideration and protective measures, such as providing point-of-use water filter/purifier units (e.g., water purifiers along the aircraft water distribution system to remove pathogenic cysts from the water moving through them). Such water filter/purifier units also remove bacteria, viruses, and other microorganisms from the water moving through them. Further, to overcome the challenges of virus and bacteria transmission via water systems and colonization within the aircraft potable water distribution systems, airlines often try to assure an adequate chlorine residual within the aircraft water supply. Even so, it is necessary to periodically “sanitize” the aircraft water distribution system, typically with a 2+ hours soak of high concentration (100 ppm) chlorine solutions. The sanitation process requires time and labor intensive removal of filtration/purification cartridges from the water filter/purifier units installed along the water lines of the water distribution system in galleys, fountains, and lavatories throughout the aircraft prior to the sanitation process. After removal of cartridges, pressure vessels must be reassembled to allow complete distribution of the sanitizing solution through the water distribution system and to prevent leakage of this highly corrosive and oxidizing sanitizing solution during the two hours sanitization soak.
Filtration/purification cartridge removal is required for at least two reasons: 1) because a high concentration of chlorine is detrimental to most filtration/purification cartridges, and 2) more importantly, because microorganisms might be sheltered in crevices and imperfections at sealing surface interfaces (ideal locations for biofilm formation) of the water filter/purifier units compromising effectiveness of the sanitizing process, thereby allowing recolonization of the distribution system. Even though sanitization is recognized as effective, typically because of the relatively high cost of the sanitizing process and the revenue lost due to the downtime of the aircraft during the sanitizing process, sanitization is performed infrequently—possibly every six months or at a convenient “A Check” or more extensive maintenance intervals when other maintenance is carried out.
After chlorine flushing and soaking for two hours, following current practices, the pressure vessels once again are opened and the same filtration/purification cartridges (or new replacement filtration/purification cartridges) are installed. Potable water is flushed throughout the aircraft water distribution system to thoroughly remove the extremely high concentration sanitizing solutions. Several hours may be required to sanitize an aircraft resulting in costs averaging upwards to hundreds of dollars per unit.
Even with periodic sanitization, bacteria may colonize various branches (legs)(water lines) of water distribution systems. Bacteria multiply rapidly, sometimes doubling in number in approximately 16 minutes. Therefore, a small number of bacteria may quickly reach infectious concentrations in water intended to be consumed, especially downstream of improperly installed/serviced water filter/purifier units employed to remove chlorine, foul tastes, and odors. Further, water filter/purifier units installed in semi-remote locations along water lines of the water distribution system often require longer than desired water distribution lines (water lines) to specific service points (e.g., locations where the water is discharged from the water distribution system). These distribution lines provide unnecessary opportunities for previously purified water to be recontaminated from inadvertent inoculation, short term bacteria multiplication or biofilm formation/shedding that may have taken place in such distribution lines downstream of the water filter/purifier units. Accordingly, it is important to provide protection against water that has been contaminated downstream of a water filter/purifier unit backflowing from downstream of a water filter/purifier unit back into the water filter/purifier unit and contaminating the portion of the filtration/purification medium (e.g., a filtration/purification cartridge) of a water filter/purifier unit thereby causing water exiting the outlet port of the filter/purifier unit to be contaminated, which would create a health risk to passengers from bacteria, viruses, and the like being transferred from contaminated water from the water distribution system.
Water boilers are typically provided along the water distribution lines of a potable water distribution system for aircraft, and are provided typically along the water distribution lines downstream of water filter/purifier units of the potable water distribution system typically at or near galleys to provide hot water for use preparing beverages like coffee and tea. If water boiler expansion pressure builds up to a dangerous level due to a water boiler overheating, and protection against backflow of water through the water filter/purifier units is provided, the water boiler expansion pressure created by the water boiler overheating creates a risk of extremely hot water blowing back along the water distribution lines between the water boiler and a water filter/purifier unit, with the pressure being released by opening a faucet, such as a cold water faucet, positioned along the water distribution lines between the water boiler and the water filter/purifier unit upstream of the water boiler, possibly resulting in the person that opened the faucet being injured by scalding hot water.
Removing the backflow protection to provide some water boiler expansion pressure relief in the potable water distribution system creates a risk that the structure of the filtration/purification medium (e.g., a filtration/purification cartridge) of a water filter/purifier unit may be damaged if exposed to such water boiler expansion pressure. Moreover, removing the backflow protection creates a risk that water contaminated downstream of the water filter/purifier unit may backflow into the water filter/purifier unit and contaminate the portion of the water filter/purifier unit downstream of the filtration/purification medium of the water filter/purifier unit, thereby causing water exiting the outlet port of the water filter/purifier unit to be contaminated, which would create a health risk to passengers from bacteria, viruses, and the like being transferred from contaminated water from the water distribution system.